WASHINGTON (AP) — The U.S. military said Wednesday that it boarded an Iranian-flagged commercial oil tanker in the Gulf of Oman that was suspected of trying to violate the American blockade.

U.S. Central Command said on social media that the M/T Celestial Sea was searched and redirected after being suspected of trying to head to an Iranian port.

It’s at least the fifth vessel to be boarded since the Trump administration began the blockade of Iranian shipping.

The military boarded the tanker after President Donald Trump said he had called off renewed military strikes on Iran in an effort to make progress in negotiations to end the war.

He said he had planned “a very major attack” for Tuesday but put it off, saying America’s allies in the Gulf asked him to wait for two to three days because they feel they are close to a deal with Iran. Trump has repeatedly set deadlines for Tehran and then backed off.

Iran has a chokehold on the Strait of Hormuz, the vital shipping lane for global oil supplies, and the U.S. military has enforced its own blockade on Iranian ports and coastline as well as seizing ships linked to Tehran further afield.

The U.S. military began the blockade in mid-April, several days into a ceasefire, in an effort to force Tehran to open the Strait of Hormuz and accept a deal to end the war. Before the U.S. blockade, Tehran had allowed some ships perceived as friendly to pass while charging considerable fees, leading to accusations it is holding the global economy hostage.

The U.S. military has said that 1,550 vessels, from 87 countries, are currently stranded in the Persian Gulf.

The disruptions to the critical waterway have led to wild shifts in the global energy market and raised gasoline prices in the United States, causing potential problems for Trump’s Republican Party ahead of congressional midterm elections in November.